This application claims the priority of German Application No. 101 35 727.3, filed Jul. 21, 2001.
The invention relates to a control valve for installation in a wobbleplate compressor with a changeable working volume, and that has an inlet for connecting it to a pressure chamber of the compressor. A first outlet is connectable to a crank chamber of the compressor. A closing element and means for acting upon the closing element are provided. The present invention is also directed to a wobbleplate compressor with a changeable working volume, in particular for use in a motor vehicle air conditioning system.
Wobbleplate compressors are used a great deal in vehicle air conditioning systems where they compress the cooling agent from the evaporator before it is supplied to a heat exchanger. Among other things, these rugged compressors have the advantage that they can also be used for compressing CO2, which for environmental reasons has mostly replaced the fluorinated hydrocarbons used in the past as cooling agents.
Different types of cooling agents, such as CO2, will in the future replace the cooling agents used so far, for example R134a, for environmental reasons. Since CO2 must be compressed considerably more as compared to the cooling agents used so far, for example by a factor of 10, to obtain a comparable cooling output, the requirements with respect to the seal between the compressor housing and the environment, for example, and the control requirements, will also increase considerably.
Modern automobiles for the most part use wobbleplate compressors with a changeable working volume. For this usage, the wobbleplate is pivotally attached to a drive shaft, so that the angle of the wobbleplate with respect to the drive axis is changeable. By changing this angle, the working volume andxe2x80x94with a given revolutionary speedxe2x80x94the compressor output is changed. As a rule, the change in the angle is achieved by changing the inside pressure of the crankshaft housing, i.e., the crank chamber.
A wobbleplate compressor and a control valve for controlling and regulating the crank chamber pressure is known from reference EP 0 748 937 A2. The valve of this publication is an electromagnetic two-way valve, which connects a pressure chamber to the crank chamber through bores. The pressure of the crank chamber pressure is changed by opening and closing this valve. In principle, the known device can be used for controlling the crank chamber pressure, but a high control speed cannot be achieved with this device. A high control speed, however, is of considerable importance for many application cases.
Starting with this prior art, it is an object of the invention to modify a control valve for a wobbleplate compressor in such a way that it is possible to achieve a high control speed. This object is solved with a control valve having a second outlet for connecting it to a suction chamber of the compressor. A closing element cooperates with the second outlet. The object is also achieved with a wobbleplate compressor having such a control valve.
According to the invention, a three-way control valve is used, which has an additional outlet that is connected to the suction chamber. This additional outlet only is acted upon by a closing element, which means that the passage between the pressure chamber and the crank chamber is continuously opened. By opening and closing the output leading to the suction chamber, low pressure is xe2x80x9cadded toxe2x80x9d the existing high pressure. A quick control is possible because the pressure differences in that case are very high.
Means for acting upon the closing element can include a coil and an armature that can move inside the coil. Thus, the closing element is indirectly acted upon by electromagnetic forces, which also contributes to a high control speed.
With a control valve having a coil that is supplied with an alternating voltage having a frequency above 100 Hz, and preferably approximately 500 Hz, a type of swimming control state can be obtained. Thus, the outlet connected to the suction chamber will never be quite open and never be quite closed. This contributes to a further increase in the control speed.
The wobbleplate compressor may have a safety valve, which connects the crank chamber to the suction chamber if the differential pressure between the crank chamber and the suction chamber exceeds a predetermined value. This configuration provides for particularly high operational safety.
The wobbleplate compressor may have piston rings arranged on the pistons. Further, the piston stroke may be larger than the piston diameter. Moreover, a pressure above 100 bar, preferably approximately 140 bar, may be generated on the high-pressure side. Further, the wobbleplate compressor may have a working volume of approximately 25-30 cm3. Such a compressor is particularly suitable for use with a CO2 air conditioning system.